Specific gravity sensor and a system employing the sensor

ABSTRACT

A specific gravity sensor that is disposed in a liquid, the sensor including at least one pair of vertically extending, light-transmitting elements, one of the elements of the pair having a light-emitting portion submerged in the liquid, which portion is spaced from a confronting light-receiving portion of the other element. Each element has a portion that extends above the liquid and one of those latter portions is subjected to light. A light-flow inhibitor is guided vertically to move upwardly and downwardly between those submerged portions of those elements depending upon the variations in the specific gravity of the liquid and the inhibitor thereby functions to permit and prevent, respectively, the transmission of light therebetween. The sensor can be employed in a system for controlling mechanism by picking up light rays that emanate from the light-receiving light-transmitting element.

United States Patent 1 Brown et al.

[ Dec. 11, 1973 SPECIFIC GRAVITY SENSOR AND A SYSTEM EMPLOYING THESENSOR [73] Assignee: The Regents of the University of California,Berkeley, Calif.

22] Filed: Jan. 4, 1971 [21] Appl. No.: 103,623

[52] US. Cl. 73/453, 250/227 [51] Int. Cl. G0ln 9/10 [58] Field ofSearch 73/32, 440, 451,

73/452, 453, 454, 307-314, 209, 293, DIG. 11; 250/227; 340/249, 282,380; 136/182; 356/201, 207, 208; 350/96 R, 96 B; 116/118 R; 33/DIG. 3;200/84 R, 84 A 211951 Cohen 731452 x 7/1970 Matzen et a1. 73/313 PrimaryExaminer-Charles A; Ruehl A ttomey-Carl R. Brown and Neil F. Martin [57]ABSTRACT A specific gravity sensor that is disposed in a liquid, thesensor including at least one pair of vertically extending,light-transmitting elements, one of the elements of the pair having alight-emlitting portion submerged in the liquid, which portion is spacedfrom a confronting light-receiving portion of the other element. Eachelement has a portion that extends above the liquid and one of thoselatter portions is subjected to light. A lightflow inhibitor is guidedvertically to move upwardly and downwardly between those submergedportions of those elements depending upon the variations in the specificgravity of the liquid and the inhibitor thereby functions to permit andprevent, respectively, the transmission of light therebetween. Thesensor can be employed in a system for controlling mechanism by pickingup light rays that emanate from the light-receiving light-transmittingelement.

15 Claims, 14 Drawing Figures PATENIEU HEB 1 1 I975 SHEET l U? 4INVENTORS DANIEL M. BROWN BY JOHN D. lSAACS mm FIG. 3

ATTORNEY PMENTEU HEBH I975 SHEET 30F 4 116 FIG. 6

INVENTORS FIG. /0 DANIEL M. BROWN BY JOHN D. ISAACS mm film/ ATTORNEYSHEET t CF 4 PATENTED DEE 1 1 1975 MN (Y OW E T N N R E M O W S T N I TI A N H AOd V Ddh o m M H/ v z/ //1 z SPECIFIC GRAVITY SENSOR AND ASYSTEM EMPLOYING THE SENSOR BACKGROUND OF THE INVENTION 1. Field of theInvention The invention is directed to a sensor for determining thespecific gravity of liquid, and to a system in which the sensor isutilized for actuating mechanism, as for example, for the charging of astorage battery by an electric generator which responds to the sensor.

2. Description of the Prior Art A search through the patented artuncovered the following patents:

ISSUE DATE PATENT N0. PATENTEE Sept. 8, 1936 2,053,353 Talbot July 27,1943 2,325,251 Knisely May 3, 1949 2,468,833 Murphy Mar. 10, 19532,631,183 Babis July 22, 1958 2,844,532 White et al. Mar. 5, 19633,079,887 Dawkins June 11, 1963 3,093,516 Hennen et a1. Mar. 7, 19673,308,366 Arpin Sept. 12, 1967 3,340,736 Suematsu Aug. 12, 19693,460,995 Webb Mar. 10, 1970 3,500,167 Applegate et al. Apr. 28, 19703,508,973 Hicks et a1.

Although these disclosures in the patented art are directed to sensors,none shows a sensor of the type in which a beam of light is interruptedby a light-flow inhibitor which lowers in liquid when the specificgravity of the liquid decreases.

SUMMARY OF THE INVENTION A light-flow inhibitor lowers and raises inresponse to decreasing and increasing, respectively, of liquid and,therefore, is capable of interrupting a beam of light. The beam of lightis conveyed through two lighttransmitting elements. These elementsextend vertically into liquid, the specific gravity of which liquid isto .be measured and controlled. The light-transmitting elements arelight shielded from one another except at selected confronting portionsthereof. A guide is provided for guiding the vertical movement of theinhibitor. When the inhibitor lowers to between the selected confrontingportions of the guide, the light beam is interrupted. Thus, by visualobservance of the light interruption, steps can be taken to observe thethen specific gravity of liquid.

The sensor can also be used in a system for automatically controllingmechanism, for example for controlling the specific gravity of acid oralkaline electrolytic cells, the position of the light-flow inhibitorcontrolling a battery-charging generator.

Other features and the advantages of the present invention will beapparent from the following description, reference being had to theaccompanying drawings wherein preferred embodiments of the invention areillustrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of the sensorembodied in a cap for a vessel, the view including also fibre optictubes, a tube for the member which is movable vertically in response tovariation in the specific gravity of liquid, a lamp and a photoelectriccell;

FIG. 2 is a top plan view of the sensor;

FIG. 3 is a sectional view of the sensor taken along .line 3-3 of FIG.1, but on a larger scale;

FIG. 4 is a longitudinal sectional view of the tube for the movablemember, said member therein and two fibre optic tubes, the view beingtaken along line 44 of FIG. 3;

FIG. 5 is a wiring diagram embodying the sensor;

FIG. 6 is a side view of a different embodiment of a sensor;

FIG. 7 is a top plan view of the sensor of FIG. 6;

FIGS. 8, 9 and 10 are sectional views taken along lines 8-8, 9--9 and10-10, respectively, of FIG. 6;

FIG. 11 is a sectional view of another embodiment of the invention;

FIG. 12 is a wiring diagram embodying the sensor as a controller for anelectric generator;

FIG. 13 is a longitudinal sectional view of still another embodiment ofthe invention, only two of the six fibre optic tubes being shown; and

FIG. 14 is a diagrammatic view of a system employing the embodimentshown in FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to theembodiment shown in FIGS. 1, 2 and 3, the sensor 10 coprises meansforming a guide 12 which, for the purpose of illustration, may be formedintegrally with a cap 14 for a vessel, as for example the cap for anelectrolytic battery. The guide 12 is closed by a bottom wall 16 and isprovided with confronting openings 18 and 20 adjacent the bottomthereof. The guide is provided also with holes 21 to insure that theliquid therein has the same specific gravity as that which surrounds theguide.

A light-flow inhibitor 22 in the form of an opaque ball is disposed inand guided vertically by the guide 12,

the diameter of the ball being slightly less than the inside diameter ofthe guide, whereby the ball can move vertically freely within the guide.The density of the ball is such that itlowers and rises in response tothe decrease and increase, respectively, of specific gravity of theliquid in which the sensor guide 12 is immersed.

Two vertically disposed light-transmitting elements 24 and 26 in theform of fibre optic tubes are disposed along the outside of the guide12. The lower exposed ends 28 and 30, respectively, of the fibre optictubes extend, respectively, into the lower, confronting openings 18 and20 in the guidel2. The upperends 32 and 34 of the tubes 24 and 26,respectively, extend through the cap 14 above the liquid.

A source of light, for example lamp36, is disposed at the upper end 32of light-transmitting tube 24. In view of the fact that the tubes 24 and26 are light-isolated from one another, except at their lower portions,and when the beam of light can travel in the space between the lowerends of the tubes 24 and 26, light emanating from the lamp 36 is visibleat the upper end 34 of tube 26. However, when a light-flow inhibitorspans the openings 18 and 20 in the guide 12, the beam is interruptedand, consequently, the light from the lamp. 36 is not visible at the end34 of light-transmitting tube 26.

Thus it is apparent that when the specific gravity of liquid, in whichthe guide 12 is immersed, lowers to. a degree in which the opaque ball22 lowers to a position in which it spans the area between theconfronting openings 18 and 20 in the guide, light cannot pass to fibreoptic tube 26, with the result that light from lamp 36 is not visible atthe upper end. 34 of tube 26.

The commercial hydrometers not present on the market require directaccess to the vessel containing the liquid, the specific gravity ofwhich is to be observed.

The present invention provides for observing from a remote positionwhether or not the specific gravity is below that which is desirable.Thus, the invention has utility in such installations in which theliquidcontaining vessel is remote from the observer.

Attempts have been made to indicate lowering of specific gravity byfloating a sensor which, when it lowers from its floating position,signifies a decreasing of specific gravity. Such sensors are notpractical for two reasons, namely: (1) the density ball must exert asufficient buoyancy force to operate a switch, resulting in therequirement of a massive float which displaces too much liquid, forexample too much electrolyte in a storage battery; and (2) a floatingindicator is subjected to the sloshing of the liquid in a movingvehicle, resulting in opening and closing of the switch unnecessarily.

In practicing the present invention, specific gravity decreasing isobserved by the sinking of the indicator and the indicator is notsubjected to sloshing of the liquid; nor need it be of such large massthat is necessary to operate switching mechanism.

In those prior art systems employing electrical equipment for testingthe voltage of an electric battery, a heavy discharge load is necessaryto obtain accurate voltage measurement. Such heavy discharge not onlydrains power from the battery, but causes undesirable arcing and failureof switches, both of which cause trouble, for example in submarines.

In practicing the visual indication principal of the present invention,switching to determine the condition of the battery is eliminated.

Referring to the embodiment shown in FIGS. 6 through 10, the sensor 110is provided with a guide 112 which is formed integrally with a cap 114for a vessel. The guide is provided with a bottom wall 116 and with apair of confronting openings 118 and 120 adjacent the bottom thereof.The guide is also provided with holes 121 thus insuring that the liquidtherein has the same specific gravity as that which surrounds the guide.

The guide is also provided with pairs of confronting openings 123-125and 127-129. The pair of confronting openings 123-125 is disposed at ahigher level and laterally of the pair of openings 118 and 120; the pairof confronting openings 127-129 is disposed at a higher level andlaterally of the pair of openings 123-425.

A light-flow inhibitor in the form of an opaque ball 122 is disposed inand guided vertically by the guide 112. The ball can move freelyvertically in the guide. Like ball 22, the density of the ball is suchthat it lowers and rises in response to decrease and increase,respectively, of the specific gravity of the liquid in which the guide112 is immersed.

Two sets of vertically disposed light-transmitting elements, in the formof fibre optic tubes, are disposed along the outside of guide 112. Oneset includes tubes 124, 135 and 137; the other set includes tubes 126,141 and 143. The lower exposed ends of tubes 124, 135 and 137 extend,respectively, into openings 118, 123 and 127 of guide 112, and the upperportions of said tubes extend through the vessel cap 114. The upper endsof those tubes are subjected to a common source of light, namely to alamp 136. The lower exposed ends of tubes 126, 141 and 143 extend,respectively, into openings 120, 125 and 129 in the guide 112. The tubesextend through the vessel cap.

When the specific gravity is highest, the ball 122 floats on the surfaceof the liquid. At that time, all of the areas between the confrontingopenings transmit light between confronting openings. Therefore, lightemanates from the outer ends of the tubes 126, 141 and 143. Should thespecific gravity decrease slowly, the beams of light emanating from theends of tubes 124, 135 and 137 will be interrupted progressively by theslow lowering of opaque ball 122. Thus when ball 122 blocks the areabetween openings 127 and 129, light fails to emanate from the end oftube 137, and therefore, light will not emanate from the end of optictube 143, but if light is emanating from the ends of tubes 124 and 135,the observer will be apprised of the fact that the specific gravity haslowered somewhat. Too, when the specific gravity decreases further, ball122 will block the area between openings 125 and 127 and light will notemanate from tube 141. However, light will now emanate from tube 143 andwill continue to emanate from tubes 126 and 143. Further decrease willcause the ball to block the area between openings 118 and 120, resultingin failure of light to emanate from optic tube 126. Finally, when theball 122 blocks the passage between openings 118 and 120, light will notemanate from the end of optic tube 126. At this time, light emanatesfrom optic tubes 141 and 143. Thus three stages of the specific gravitycan be observed visually.

Referring now to the embodiment shown in FIG. 11, the guide 112 and cap114 are like those shown in FIGS. 6 through 10, but for simplicity ofillustration, the tubes 141, 135, 143 and 137 are not shown as beingstaggered. In addition to ball 122, the sensor includes two moresubstantially opaque balls 147 and 149. Each of these balls havedifferent densities. The density of ball 147 is less than that of ball122; and the density of ball 149 is less than that of ball 147. Allballs are buoyed upwardly when the specific gravity is highest. A slightdecrease in gravity causes ball 122 to block the lowermost area in theguide, i.e. the area between the openings 118 and 120. Further slightdecrease will cause ball 147 to block the area between openings 123 anda still further decrease will cause ball 149 to block the area betweenopenings 127 and 129. Thus, upon continuous decreasing of specificgravity, the lights from optic tubes 126, 141 and 143 will beextinguished sequentially, resulting in apprising the observer of thespecific gravities of the liquid.

ln many cases it is desirable that the specific gravity of the liquid beutilized to operate mechanism for controlling the specific gravity ofthe liquid or for operating a visible signal or signals or an audiblesignal or signals. In FIGS. 1, 2 and 3, a photoelectric cell can be usedto discern whether or not light is emanating from fibre optic tube 26.As shown diagrammatically in FIG. 5, a photoelectric cell 38 is utilizedto control an electric control block 40 which is supplied with currentfrom a battery 42. When no light emanates from fibre optic tube 26, thesignal from the cell 38 is interrupted resulting in the control blocksenergization of a coil 44 to close a switch 46. This switch connects anautomobile type engine starting motor 48 to battery 42. Motor 48 cranksan engine 50 to drive a battery charging generating device 52 to theelectrolytic type battery 54. A

solenoid actuated switch 56 is connected across the generating deviceand switch 56 functions to disconnect the starting motor 48 after thevoltage of the generating device attains a predetermined value. Thegenerating of current will continue until the operator is satisfied thatthe battery is fully charged, at which time light will be emanating fromthe fibre optic tube 26. The engine can then be stopped manually.

As shown in the diagrammatic view in FIG. 12, the system employs thesensor 110 shown in FIGS. 6 through 10. In that embodiment, threephotoelectric cells 138, 153 and 155 are employed and are responsivesequentially to the lights emanating from fibre optic tubes 1 13, 141and 126.

When, for example, the liquid is an electrolyte of a storage battery,the system can control the specific gravity of the batteryautomatically. Such system is shown in FIG. 12, where the sensor 1111,through ball 122, controls the photoelectric cells 138, 153 and 155,which cells sequentially control field windings 165, 167 and 169 of anelectric current generating device 152. Thus, if the specific gravity ofthe battery is at its extreme low stage, at which stage ball 122 isblocking the openings 118 and 1211, the current output of the generatingdevice is at its full capacity in that all windings are effective. Asthe specific gravity increases and the ball 122 rises, the fieldwindings will be progressively disconnected due to the progressiveblocking by ball 122 of the areas between the openings 123125 and127-129. When the ball rises to its highest position, all photoelectriccells are activated to stop the motor (engine 150) which drives thecurrent generating device 152.

Referring more specifically to FIG. 12, the energizations ofphotoelectric cells 138, 153 and 155 are through light emanating fromfibre optic tubes 126, 141 and 1413, respectively. As long as light isemanating from the optic tubes, the generator 152 is active. When thespecific gravity of the electrolyte inbattery 154 is below apredetermined value, ball 122 will block openings 118 and 12b and thephotoelectric cell 138 will be inactive. This inactivity will render theelectric control block 1411 active through battery 142 to effectenergization of switch coil M1 to close switch 146. The closing ofswitch. 146 closes the circuit to the automobile type starting motor 111that then starts the engine 150, the ignition being supplied through atransformer 158. The engine drives the generator 152 through a shaft160. When the voltage across the generator attains a predeterminedvalue, electromagnetic switch 156 will interrupt the circuit to coil 144whereby switch 146 will open to interrupt the flow of current to thestarting motor 148.

When the specific gravity is low, all field cois 165, 167 and 169 areenergized to supply the full current output to the battery. After thespecific gravity increases to a predetermined value, the ball 122 willmove upwardly and block the confronting openings 123 and 125 in theguide 112, resulting in the cessation of light emanation from optic tube141 and cell 153 will become ineffective. Such ineffectiveness is sensedby the electric control block 1410 to cause a current flow to a solenoidswitch 171 whichthen disconnects the generator coil 165 therebydecreasing the current output of the generator. Further increase inspecific gravity of the electrolyte in battery 151 causes ball 122 toblock the confronting openings 127 and 128, resulting in cessation oflight emanation from cell 155. This results in the energization ofsolenoid switch 171, which energization disconnects generator coil 173,resulting in further decreasing of current output of the generator.

From the foregoing it will be apparent that the charging rate of thegenerator is decreased as the specific gravity of the electrolyteincreases. Such decreasing is highly desirable.

When the battery 154 is fully charged, the ball is above the confrontingopenings 127 and 129 of the guide, whereby light emanates from all optictubes 126, 141 and 145. The activation of photoelectric cell 153 effectsclosing of a solenoid switch 175 when field coil 169 is renderedineffective and the generator ceases to function as such. The cessationof the flow of current effects reclosing of solenoid switch 156 and alsoeffects the discontinuance of current flow through coil 144 of switch146 whereby the ignition transformer is rendered ineffective. v

The same phenomenon takes place when a plurality of balls are employedsuch as ballls 122, 147 and 149 that are shown in FIGS. 6 through 10 anddiagrammatically shown in FIG. 12. When the battery electrolyte is toolow, all of the balls will have sunk to their lowermost position inwhich ball 122 blocks the area between openings 118 and 120, ball 147blocks the area between openings 123 and and ball 149 blocks the areabetween openings 127 and 129. When those openings are blocked, all fieldwindings will be effected, and as the top ball 149 rises, due toincrease in specific gravity, one of the field windings is renderedineffective. Upon further rises in specific gravity, ball 147,

rises, and then ball 122 rises, sequentially, to render the other twowindings ineffective, sequentially. When the battery is fully charged,all photoellectric cells are effective and the motor for driving thecurrent generating device is rendered ineffective.

Referring to the embodiment shown in FIG. 13, which is utilized forexample for controlling a well pump, that embodiment includes a sealedcasing 60 which is connected to a cable 62 and suspended in the wellfrom which a liquid such as water is withdrawn by a pump. A battery orcircuit block 64, a lamp 66 and a photoelectric cell 68 are disposed inthe casing 60. Wires 711 are connected with the cell 68. These wiresextend through a stuffingbox 72 to above the ground level.

A cage 74 is suspended from the bottom of casing 60 and a sensor 76 likethat shown in FIGS. 6 through 10 is disposed in the casing. The systemfunctions substantially as explained within the description of FIG. 12,except that the sensor controls a pump which is withdrawing, forexample, water from a well. The sensor 76 controls the output of a pump78, shown diagrammatically in FIG. 141 through a standard typecharge-rate controller 811.

Should the specific gravity increase in the water, for example if saltwater entered the well, the raising of the ball actuates switchessequentially to decrease the pumping action of the pump to therebydecrease the withdrawing of salty water from the area about the well.When all the balls are at their highest positions, the photoelectriccell will function to stop the pumping action.

One form of pump control, forillustrativepurpose, is shown in FIG. 14wherein one form of rate control 80 for a motor 84 includes apotentiometer 82, the movable contact 86 being controlled by threesolenoids 88, 90 and 92. These solenoids are controlled through theelectric control block 94 which in turn is controlled by thephotoelectric cells 138, 153 and 155 as explained with respect to FIG.12. Thus the output of the pump 78 is controlled by the speed of themotor 84.

The bottom wall of the sensor 76 is in the form of a removable plug 96whereby balls of different densities can be exchanged.

From the foregoing it is apparent that the sensors of the presentinvention function entirely different from those of the prior art. Thesensors achieve results that are more beneficial and less expensive thanthose of the I prior art.

Having described our invention, we claim:

1. A sensor for determining specific gravity, said sen- SOI' comprising:

A. means extendable into liquid that is to be tested for determining thespecific gravity thereof, said means forming a guide, said guide havingconfronting openings;

a plurality of vertically extending, lighttransmitting rods, said rodshaving spaced and confronting portions at said openings in the guide,each of said rods having a portion extending above the liquid;

C. an opaque hydrometer guided by said means into and out of the areabetween said openings in the means;

D. means forming a source of light disposed for transmitting light tothe portion of one of the rods that is disposed above the liquid.

2. A sensor as defined in claim 1, characterized in that the confrontingopenings in said means are immersed in the liquid to be tested.

3. A sensor as defined in claim 1, characterized in that the confrontingopenings in said means are adjacent the lower end thereof.

4. A sensor as defined in claim 1, characterized to include:

E. a cap for a vessel, said rods, said first mentioned means, saidhydrometer and said cap forming a unit.

5. A system for controlling specific gravity, said system comprising:

A. means extendable into liquid that is to be tested for determining thespecific gravity thereof, said means forming a guide, said guide havingconfronting openings adjacent the upper end thereof;

a plurality of vertically extending, lighttransmitting rods, said rodshaving spaced and confronting portions at said openings in the guide,each of said rods having a portion extending above the liquid;

C. an opaque hydrometer guided by said means into and out of the areabetween said openings in the means;

D. means forming a source of light disposed for transmitting light tothe portion of one of the rods that is disposed above the liquid;

E. light sensitive means responsive to the light emanating from thatportion of the other of said lighttransmitting rods that is above theliquid.

6. A system as defined in claim 5, characterized in that the lightsensitive means is an electric generator controller, and furthercharacterized to include:

F. an electric current generator;

G. an electrolytic cell having negative and positive electrodesconnected with the generator;

H. and means controlled by the generator controller for driving thegenerator.

7. A system as defined in claim 5, characterized to include:

F. a cap for a vessel, said rods, said first mentioned means, saidhydrometer andsaid cap forming a unit.

8. A sensor for determining specific gravity, said sensor comprising:

A. means extendable into liquid that is to be tested for variations inspecific gravity thereof, said means forming a guide and having pairs ofconfronting openings, one pair being disposed at a higher level than theother pair;

a plurality of vertically extending, lighttransmitting rods, one of saidrods having a portion disposed in light-transmitting relationship withthe upper opening of a pair of openings, and another of said rods havinga portion disposed in lighttransmitting relationship with the loweropening of a pair of openings, each of said rods having a portionextending above the liquid;

C. a second plurality of vertically extending, lighttransmitting rods,one of the latter rods having a portion disposed in light-receivingrelationship with the upper opening of the first mentioned pair ofopenings, another of the latter rods having a portion disposed inlight-receiving relationship with the lower opening of the secondmentioned pair of openings, each of said rods having a portion extendingabove the liquid;

D. an opaque hydrometer guided by said means into and out of the areabetween said openings in the means;

E. a second opaque hydrometer guided by said means into and out of thearea between the openings in said means, the density of the secondmentioned hydrometer being less than that of the first mentionedhydrometer and disposed above the first mentioned hydrometer;

F. means forming a source of light disposed for transmitting light tothe portions of the rods that are disposed above the liquid.

9. A sensor as defined in claim 8, characterized in that the openings ofthe first pair of openings in the means are disposed laterally of thesecond pair of openings in the means.

10. A sensor as defined in claim 8, characterized to include:

F. a cap for a vessel, said first mentioned means, saidlight-transmitting rods, said opaque hydrometers and the cap forming aunit.

11. A system for controlling specific gravity, said system comprising:

A. means extendable into liquid that is to be tested for variations inspecific gravity thereof, said means forming a guide and having pairs ofconfronting openings, one pair being disposed at a higher level than theother pair;

a plurality of vertically extending, lighttransmitting rods, one of saidrods having a portion disposed in light-transmitting relationship withthe upper opening ofa pair of openings, another of said rods having aportion disposed in light-transmitting relationship with the loweropening of a pair of openings, each of said rods having a portionextending above the liquid;

C. a second plurality of vertically extending, lighttransmitting rods,one of the latter rods having a portion disposed in light-receivingrelationship with the upper opening of the first mentioned pair ofopenings, another of the latter rods having a por tion disposed inlightreceiving relationship with the lower opening of the secondmentioned pair of openings, each of said rods having a portion extendingabove the liquid;

D. an opaque hydrometer guided by said means into and out of the areabetween said openings in said means;

E. a second opaque hydrometer guided by said means into and out of thearea between the openings in said means, the density of the secondmentioned hydrometer being less than that of the first mentionedhydrometer and disposed above the first mentioned hydrometer;

F. means forming a source of light for transmitting light to the outerportions of those lighttransmitting rods employed for transmitting lightinto the openings in said means;

G. light sensitive means responsive to the light emanating from outerportions of those lighttransmitting rods employed for transmitting lightfrom the openings in said first mentioned means. 12. A system as definedin claim 11, characterized in that the light sensitive means is anelectric generator controller; and further characterized to include:

H. an electric current generator;

I. an electrolytic cell having negative and positive electrodesconnected with the generator;

J. and means responsive to the generator controller for driving thegenerator.

13. A system as defined in claim 12, characterized to include:

include:

N. a cage attached to said casing, said guide and hydrometer beingdisposed in the cage.

15. A system for controlling specific gravity, said system comprising:

A. means extendable into liquid that is to be tested for variations inspecific gravity thereof, said means forming a guide and having pairs ofconfronting openings, one pair being disposed at a higher level than theother pair;

B. a plurality of vertically extending, lighttransmitting rods, one ofsaid rodshaving a portion disposed in light-transmitting relationshipwith the upper opening of a pair of openings, another of said rodshaving a portion disposed. in light-transmitting relationship with thelower opening of a pair of openings, each of said rods having a portionextending above the liquid;

C. a second plurality of vertically extending, lighttransmitting rods,one of the latter rods having a portion disposed in light-receivingrelationship with the upper opening of the first mentioned pair ofopenings, another of the latter rods having a portion disposed inlight-receiving relationship with the lower opening of the secondmentioned pair of openings, each of said rods having a portion extendingabove the liquid;

D. an opaque hydrometer guided by said means into and out of the areabetween said openings in said means; I

E. a second opaque hydrometer guided by said means into and out of thearea between the openings in said means, the density of the secondmentioned hydrometer being less than that of the first mentionedhydrometer and disposed above the first mentioned hydrometer;

F. means forming a source of light for transmitting light to the outerportions of those lighttransmitting rods employed for transmitting lightinto the openings in said means;

G. light sensitive means responsive to the light emanating from outerportions of those lighttransmitting rods employed for transmitting lightfrom the openings in said means;

H. a sealed casing, said means (F) and (G) disposed in the casing;

I. signal transferring means associated with the means (G) and extendingout of the casing;

J. means for supporting the casing in the liquid;

K. energy creating means outside of the liquid for controlling thesignal transferring means (I).

1. A sensor for determining specific gravity, said sensor comprising: A.means extendable into liquid that is to be tested for determining thespecific gravity thereof, said means forming a guide, said guide havingconfronting openings; B. a plurality of vertically extending,light-transmitting rods, said rods having spaced and confrontingportions at said openings in the guide, each of said rods having aportion extending above the liquid; C. an opaque hydrometer guided bysaid means into and out of the area between said openings in the means;D. means forming a source of light disposed for transmitting light tothe portion of one of the rods that is disposed above the liquid.
 2. Asensor as defined in claim 1, characterized in that the confrontingopenings in said means are immersed in the liquid to be tested.
 3. Asensor as defined in claim 1, characterized in that the confrontingopenings in said means are adjacent the lower end thereof.
 4. A Sensoras defined in claim 1, characterized to include: E. a cap for a vessel,said rods, said first mentioned means, said hydrometer and said capforming a unit.
 5. A system for controlling specific gravity, saidsystem comprising: A. means extendable into liquid that is to be testedfor determining the specific gravity thereof, said means forming aguide, said guide having confronting openings adjacent the upper endthereof; B. a plurality of vertically extending, light-transmittingrods, said rods having spaced and confronting portions at said openingsin the guide, each of said rods having a portion extending above theliquid; C. an opaque hydrometer guided by said means into and out of thearea between said openings in the means; D. means forming a source oflight disposed for transmitting light to the portion of one of the rodsthat is disposed above the liquid; E. light sensitive means responsiveto the light emanating from that portion of the other of saidlight-transmitting rods that is above the liquid.
 6. A system as definedin claim 5, characterized in that the light sensitive means is anelectric generator controller, and further characterized to include: F.an electric current generator; G. an electrolytic cell having negativeand positive electrodes connected with the generator; H. and meanscontrolled by the generator controller for driving the generator.
 7. Asystem as defined in claim 5, characterized to include: F. a cap for avessel, said rods, said first mentioned means, said hydrometer and saidcap forming a unit.
 8. A sensor for determining specific gravity, saidsensor comprising: A. means extendable into liquid that is to be testedfor variations in specific gravity thereof, said means forming a guideand having pairs of confronting openings, one pair being disposed at ahigher level than the other pair; B. a plurality of verticallyextending, light-transmitting rods, one of said rods having a portiondisposed in light-transmitting relationship with the upper opening of apair of openings, and another of said rods having a portion disposed inlight-transmitting relationship with the lower opening of a pair ofopenings, each of said rods having a portion extending above the liquid;C. a second plurality of vertically extending, light-transmitting rods,one of the latter rods having a portion disposed in light-receivingrelationship with the upper opening of the first mentioned pair ofopenings, another of the latter rods having a portion disposed inlight-receiving relationship with the lower opening of the secondmentioned pair of openings, each of said rods having a portion extendingabove the liquid; D. an opaque hydrometer guided by said means into andout of the area between said openings in the means; E. a second opaquehydrometer guided by said means into and out of the area between theopenings in said means, the density of the second mentioned hydrometerbeing less than that of the first mentioned hydrometer and disposedabove the first mentioned hydrometer; F. means forming a source of lightdisposed for transmitting light to the portions of the rods that aredisposed above the liquid.
 9. A sensor as defined in claim 8,characterized in that the openings of the first pair of openings in themeans are disposed laterally of the second pair of openings in themeans.
 10. A sensor as defined in claim 8, characterized to include: F.a cap for a vessel, said first mentioned means, said light-transmittingrods, said opaque hydrometers and the cap forming a unit.
 11. A systemfor controlling specific gravity, said system comprising: A. meansextendable into liquid that is to be tested for variations in specificgravity thereof, said means forming a guide and having pairs ofconfronting openings, one pair being disposed at a higher level than theother pair; B. a plurality of vertically extending, light-traNsmittingrods, one of said rods having a portion disposed in light-transmittingrelationship with the upper opening of a pair of openings, another ofsaid rods having a portion disposed in light-transmitting relationshipwith the lower opening of a pair of openings, each of said rods having aportion extending above the liquid; C. a second plurality of verticallyextending, light-transmitting rods, one of the latter rods having aportion disposed in light-receiving relationship with the upper openingof the first mentioned pair of openings, another of the latter rodshaving a portion disposed in light-receiving relationship with the loweropening of the second mentioned pair of openings, each of said rodshaving a portion extending above the liquid; D. an opaque hydrometerguided by said means into and out of the area between said openings insaid means; E. a second opaque hydrometer guided by said means into andout of the area between the openings in said means, the density of thesecond mentioned hydrometer being less than that of the first mentionedhydrometer and disposed above the first mentioned hydrometer; F. meansforming a source of light for transmitting light to the outer portionsof those light-transmitting rods employed for transmitting light intothe openings in said means; G. light sensitive means responsive to thelight emanating from outer portions of those light-transmitting rodsemployed for transmitting light from the openings in said firstmentioned means.
 12. A system as defined in claim 11, characterized inthat the light sensitive means is an electric generator controller; andfurther characterized to include: H. an electric current generator; I.an electrolytic cell having negative and positive electrodes connectedwith the generator; J. and means responsive to the generator controllerfor driving the generator.
 13. A system as defined in claim 12,characterized to include: K. light sensitive means responsive to thelight emanating from said other light-transmitting rod for controllingsaid electric generator controller; L. means forming a source of currentfor the means that forms the source of light; M. a sealed casing, saidmeans (F) and (G) being disposed in said casing.
 14. A system as definedin claim 13, characterized to include: N. a cage attached to saidcasing, said guide and hydrometer being disposed in the cage.
 15. Asystem for controlling specific gravity, said system comprising: A.means extendable into liquid that is to be tested for variations inspecific gravity thereof, said means forming a guide and having pairs ofconfronting openings, one pair being disposed at a higher level than theother pair; B. a plurality of vertically extending, light-transmittingrods, one of said rods having a portion disposed in light-transmittingrelationship with the upper opening of a pair of openings, another ofsaid rods having a portion disposed in light-transmitting relationshipwith the lower opening of a pair of openings, each of said rods having aportion extending above the liquid; C. a second plurality of verticallyextending, light-transmitting rods, one of the latter rods having aportion disposed in light-receiving relationship with the upper openingof the first mentioned pair of openings, another of the latter rodshaving a portion disposed in light-receiving relationship with the loweropening of the second mentioned pair of openings, each of said rodshaving a portion extending above the liquid; D. an opaque hydrometerguided by said means into and out of the area between said openings insaid means; E. a second opaque hydrometer guided by said means into andout of the area between the openings in said means, the density of thesecond mentioned hydrometer being less than that of the first mentionedhydrometer and disposed above the first mentioned hydrometer; F. meansforming a source of light for Transmitting light to the outer portionsof those light-transmitting rods employed for transmitting light intothe openings in said means; G. light sensitive means responsive to thelight emanating from outer portions of those light-transmitting rodsemployed for transmitting light from the openings in said means; H. asealed casing, said means (F) and (G) disposed in the casing; I. signaltransferring means associated with the means (G) and extending out ofthe casing; J. means for supporting the casing in the liquid; K. energycreating means outside of the liquid for controlling the signaltransferring means (I).